Impact of intrinsic alignments on cosmic shear

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Impact of intrinsic alignments on cosmic shear
Sarah Bridle, UCL (London)

• Shearing by elliptical galaxy halos
• SB Filipe Abdalla astro-ph/0608002
• Intrinsic alignments and photozs
• SB Lindsay King arXiv0705.0166
• Cluster counts and cosmic shear double
  counting?
• Masahiro Takada SB arXiv0705.0163

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Cosmic shear (2 point function)
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Cosmic shear Face-on view
Gravitationally sheared
Gravitationally sheared
Lensing by dark matter causes galaxies to appear
aligned
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Intrinsic alignments (II)
Croft Metzler 2000, Heavens et al 2000,
Crittenden et al 2001, Catelan et al 2001, Mackey
et al, Brown et al 2002, Jing 2002, Hui Zhang
2002
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Intrinsic alignments (II) Face-on view
Intrinsically Aligned (I)
Intrinsically Aligned (I)
Tidal stretching causes galaxies to align Adds to
cosmic shear signal
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Intrinsic-shear correlation (GI)
Hirata Seljak 2004 See also Heymans et al 2006,
Mandelbaum et al 2006, Hirata et al 2007
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Intrinsic-shear correlation (GI) Face-on view
Gravitationally sheared (G)
Intrinsically aligned (I)
Galaxies point in opposite directions Partially
cancels cosmic shear signal
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Cosmic shear two point tomography
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Cosmic shear tomography
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Effect on cosmic shear of changing w by 1
Cosmic Shear
Intrinsic Alignments (IA)
Normalised to Super-COSMOS Heymans et al 2004
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Effect on cosmic shear of changing w by 1
If consider only w then IA bias on w is 10
If marginalise 6 cosmological parameters then IA
bias on w is 100 (/- 1 !)
Intrinsic Alignments (IA)
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Elliptical galaxy-galaxy lensing
Bridle Abdalla
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Elliptical galaxy-galaxy lensing Face-on view
Bridle Abdalla
Background galaxy is gravitationally sheared
tangentially around foreground lens
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Bridle Abdalla
Contribution to ellipticity correlation
function Average shear around circular annulus
Does not average to zero ?net contamination
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z10.3 z20.8
Cosmic shear signal
Bridle Abdalla
Shear correlation function
Average over population visible to R24
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z10.3 z20.8
Cosmic shear signal
Bridle Abdalla
Shear correlation function
Average over population visible to R24
Change in cosmic shear signal for ? w 0.05
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Removal of intrinsic alignments

• Intrinsic intrinsic (II)
• Weight down close pairs (King Schneider 2002,
  Heymans Heavens 2003, Takada White 2004)
• Fit parameterized models (King Schneider 2003)
• Shear intrinsic (GI)
• Fit parameterized models (King 2005, Bernstein
  DETF)
• Redshift weighting (Schneider talk)

Redshift quality is crucial!
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Perfect redshifts
Least flexible model considered FoM is improved!
Redshift dependence of IA ( bins) 2 3 5
No Intrinsic Alignments
Dark energy Figure of Merit
Reasonable model? (14 IA pars) Similar FoM to no
IA case
Very flexible (100 IA pars) FoM is roughly halved
Scale dependence of IA ( bins)
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Perfect redshifts
Redshift dependence of IA ( bins) 2 3 5
Dark energy Figure of Merit
Scale dependence of IA ( bins)
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Realistic photozs sz0.05(1z)
Redshift dependence of IA ( bins) 2 3 5
Dark energy Figure of Merit
Scale dependence of IA ( bins)
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No Intrinsic Alignments
FoM / FoM(specz)
Relatively flat
(e.g. Hu 1999, Ma, Hu, Huterer 2006, Jain et al
2007, Amara Refregier 2007 ....)
Photoz error sz / (1z)
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Reasonable model? (14 IA pars)
Very flexible (100 IA pars)
FoM / FoM(specz)
Photoz error sz / (1z)
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A factor of 3 better photozs required!
0.8
FoM / FoM(specz)
0.02 (1z)
0.08 (1z)
Photoz error sz / (1z)
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Conclusions

• Lensing by elliptical galaxy halos contributes to
  shear-intrinsic term (GI)
• 3x better photozs required to remove intrinsic
  alignments
• Cluster counts and lensing power spectra very
  complementary

AD
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Survey closes this Sunday
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END
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Shearing by elliptical galaxy halos

• Plan
• Calculate shear from elliptical halo
• Calculate contribution to shear correlation fn
• Average over a population of lenses
• Compare with cosmic shear signal
• Consider effect of halo profile
• Investigate redshift dependence

Bridle Abdalla 2007
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z10.3 z20.8
Cosmic shear signal
NFW
Shear correlation function
Average over population visible to R24

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z10.3 z20.8
Cosmic shear signal
Singular isothermal ellipsoid
NFW
Shear correlation function
Average over population visible to R24

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zlens0.3 zsource0.8
Bridle Abdalla
M2001x1012 h-1 Mo
Shear correlation function
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How good to photozs need to be to remove
intrinsic alignments?

• Plan
• Remove GI, II by marginalising over some flexible
  model
• Look at the effect of GI, II on dark energy
  errors
• Dependence on flexibility of model?
• Dependence on photoz errors?

Bridle King 2007
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sz / (1z)
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Dark energy from cluster counts and lensing
including the full covariance

• Plan
• Motivation combining constraints
• Shear power spectrum is from halos
• Calculate covariance between cc and cs
• Compare with toy model
• Calculate signal to noise
• Calculate effect on dark energy error bars

Takada Bridle 2007
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A toy model

• Cluster counts
• Lensing power spectrum

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Full calculation
Toy model
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100
Toy model
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Cross correlation coefficient r
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100
Toy model
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Cross correlation coefficient r
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Full calculation
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